bims-unfpre Biomed News
on Unfolded protein response
Issue of 2023‒03‒26
seven papers selected by
Susan Logue
University of Manitoba

  1. bioRxiv. 2023 Mar 11. pii: 2023.03.10.532109. [Epub ahead of print]
      Stress preconditioning occurs when transient, sublethal stress events impact an organism's ability to counter future stresses. Although preconditioning effects are often noted in the literature, very little is known about the underlying mechanisms. To model preconditioning, we exposed a panel of genetically diverse Drosophila melanogaster to a sublethal heat shock and measured how well the flies survived subsequent exposure to endoplasmic reticulum (ER) stress. The impact of preconditioning varied with genetic background, ranging from dying half as fast to four and a half times faster with preconditioning compared to no preconditioning. Subsequent association and transcriptional analyses revealed that histone methylation, transcriptional regulation, and immune status are all candidate preconditioning modifier pathways. Strikingly, almost all subunits (7/8) in the Set1/COMPASS complex were identified as candidate modifiers of preconditioning. Functional analysis of Set1 knockdown flies demonstrated that loss of Set1 led to the transcriptional dysregulation of canonical ER stress genes during preconditioning. Based on these analyses, we propose a model of preconditioning in which Set1 helps to establish an interim transcriptional 'memory' of previous stress events, resulting in a preconditioned response to subsequent stress.Author Summary: Stress preconditioning occurs when a history of previous stresses impacts an organism's response to subsequent stresses. There are many documented cases of stress preconditioning, but the specific genes and pathways involved in the process are not well understood. Here, we take advantage of the natural genetic variation in the Drosophila Genetic Reference Panel to examine the role genetic variants play in modifying preconditioning outcomes. Our goal is to identify genes that contribute to the underlying mechanisms of preconditioning. Specifically, we measured preconditioning outcomes as the change in death rates of Drosophila on constant endoplasmic reticulum (ER) stress with and without heat stress preconditioning for each strain. We demonstrate that preconditioning outcomes are highly dependent on genetic background. Through association and transcriptional analyses, we found that histone methylation, transcriptional regulation, and immune status are all candidate pathways impacting preconditioning. Functional studies utilizing Set1 knockdown flies demonstrated that Set1, a histone H3 lysine 4 (H3K4) methyltransferase enzyme, is critical for the proper expression of a subset of ER stress genes during preconditioning. Our data indicate that Set1 likely aids in creating a transient transcriptional 'memory' following initial stress that impacts the response to subsequent stress.
  2. PNAS Nexus. 2023 Mar;2(3): pgad050
      Patients' suffering from large or deep wounds caused by traumatic and/or thermal injuries have significantly lower chances of recapitulating lost skin function through natural healing. We tested whether enhanced unfolded protein response (UPR) by expression of a UPR transcriptional activator, X-box-binding protein 1 (XBP1) can significantly promote wound repair through stimulating growth factor production and promoting angiogenesis. In mouse models of a second-degree thermal wound, a full-thickness traumatic wound, and a full-thickness diabetic wound, the topical gene transfer of the activated form of XBP1 (spliced XBP1, XBP1s) can significantly enhance re-epithelialization and increase angiogenesis, leading to rapid, nearly complete wound closure with intact regenerated epidermis and dermis. Overexpression of XBP1s stimulated the transcription of growth factors in fibroblasts critical to proliferation and remodeling during wound repair, including platelet-derived growth factor BB, basic fibroblast growth factor, and transforming growth factor beta 3. Meanwhile, the overexpression of XBP1s boosted the migration and tube formation of dermal microvascular endothelial cells in vitro. Our functional and mechanistic investigations of XBP1-mediated regulation of wound healing processes provide novel insights into the previously undermined physiological role of the UPR in skin injuries. The finding opens an avenue to developing potential XBP1-based therapeutic strategies in clinical wound care protocols.
    Keywords:  X-box-binding protein 1; gene transfer; growth factors; unfolded protein response; wound healing
  3. FEBS J. 2023 Mar 23.
      The endoplasmic reticulum (ER) is the organelle where the production and shaping of most secreted and transmembrane proteins happens. ER function is finely regulated to prevent accumulation of misfolded proteins generating ER stress. ER stress is common in both healthy and pathological situations due to multiple intrinsic and extrinsic factors including acute demand in protein synthesis, hypoxia or impaired protein folding caused by gene mutations. Sayyad et al. found that the M98K mutation of optineurin sensitizes glaucoma retinal ganglion cells to ER stress-induced cell death. This is associated with an autophagy-dependent elevation of ER stress sensor expression.
    Keywords:  ER stress; autophagy; cell death; glaucoma; optineurin
  4. Exp Lung Res. 2023 Mar 22. 1-9
      Purpose: Alveolar epithelium dysfunction is associated with a very large spectrum of disease and an abnormal repair capacity of the airway epithelium has been proposed to explain the pathogenesis of Idiopathic Pulmonary Fibrosis (IPF). Following epithelium insult, the damaged cells will activate pathways implicated in the repair process, including proliferation and acquisition of migratory capacities to cover the denuded basement membrane. Induction of Endoplasmic Reticulum stress may be implicated in this process. Interestingly, ER stress excessive activation has been proposed as a central event associated with aberrant repair process and cellular dysfunction observed in IPF. Methods: We study by wound healing assay the molecular targets associated with Alveolar Epithelial Cells (AEC) repair. Results: We demonstrate that the wound recovery of AEC is associated with TGF-β1 signaling and increased transcriptional activity of ER stress and HIF-dependent genes. We further demonstrated that inhibition of TGF-β1 signaling, CHOP expression or HIF-1 expression, limits AECs wound closure. Conclusion: the use of pharmacological drugs targeting the ER/HIF-1 axis could be an attractive approach to limit AEC dysregulation in pathological condition, and confirmed a critical role of theses factor in response to alveolar injury.
    Keywords:  Alveolar epithelial cell; ER stress; repair
  5. bioRxiv. 2023 Mar 12. pii: 2023.03.11.532186. [Epub ahead of print]
      The integrated stress response (ISR) is a network of eIF2 α kinases, comprising PERK, GCN2, HRI, and PKR, that induce translational and transcriptional signaling in response to diverse insults. The PERK ISR kinase regulates mitochondria in response to endoplasmic reticulum (ER) stress. Deficiencies in PERK signaling lead to mitochondrial dysfunction and contribute to the pathogenesis of numerous diseases. We define the potential for pharmacologic activators of other ISR kinases to rescue ISR signaling and promote mitochondrial adaptation in cells lacking PERK. We show that the HRI activator BtdCPU and the GCN2 activator halofuginone activate ISR signaling and restore ER stress sensitivity in Perk- deficient cells. However, these compounds differentially impact mitochondria. BtdCPU induces mitochondrial depolarization, leading to mitochondrial fragmentation and ISR activation through the OMA1-DELE1-HRI signaling axis. In contrast, halofuginone promotes mitochondrial elongation and altered mitochondrial respiration, mimicking the regulation induced by PERK. This shows halofuginone can compensate for deficiencies in PERK activity and promote adaptive mitochondrial remodeling, highlighting the potential for pharmacologic ISR activation to mitigate mitochondrial dysfunction and motivating the pursuit of highly-selective ISR activators.
  6. ACS Chem Biol. 2023 Mar 22.
      Soluble epoxide hydrolase (sEH) is a bifunctional enzyme responsible for lipid metabolism and is a promising drug target. Here, we report the first-in-class PROTAC small-molecule degraders of sEH. Our optimized PROTAC selectively targets the degradation of cytosolic but not peroxisomal sEH, resulting in exquisite spatiotemporal control. Remarkably, our sEH PROTAC molecule has higher potency in cellular assays compared to the parent sEH inhibitor as measured by the significantly reduced ER stress. Interestingly, our mechanistic data indicate that our PROTAC directs the degradation of cytosolic sEH via the lysosome, not through the proteasome. The molecules presented here are useful chemical probes to study the biology of sEH with the potential for therapeutic development. Broadly, our results represent a proof of concept for the superior cellular potency of sEH degradation over sEH enzymatic inhibition, as well as subcellular compartment-selective modulation of a protein by PROTACs.
  7. Antioxid Redox Signal. 2023 Mar 21.
      εβOrganisms adapt to changing environments by engaging cellular stress response pathways that serve to restore proteostasis and enhance survival. A primary adaptive mechanism is the Integrated stress response (ISR), which features phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2). Four eIF2α kinases respond to different stresses, enabling cells to rapidly control translation to optimize management of resources and reprogram gene expression for stress adaptation. Phosphorylation of eIF2α blocks its guanine nucleotide exchange factor, eIF2B, thus lowering the levels of eIF2•GTP required to deliver initiator tRNA to ribosomes. While bulk mRNA translation can be sharply lowered by heightened phosphorylation of eIF2α, there are other gene transcripts whose translation is unchanged or preferentially translated. Among the preferentially translated genes is ATF4, which directs transcription of adaptive genes in the ISR. This review focuses on how eIF2α kinases function as first responders of stress, the mechanisms by which eIF2α phosphorylation and other stress signals regulate the exchange activity of eIF2B, and the processes by which the ISR triggers differential mRNA translation. The ISR is tunable and integrates with other stress pathways to optimize adaptation. To illustrate the synergy between stress pathways, we describe the mechanisms and functional significance of communication between the ISR and another key regulator of translation, mTORC1, during acute and chronic amino acid insufficiency. Finally, we discuss the pathological conditions that stem from aberrant regulation of the ISR, as well as therapeutic strategies targeting the ISR to alleviate disease.